The benefits of using a Digital mastering engineer go further than the engineer's talents. The equipment and space that make up the mastering studio are just as important. Most people have seen recording studios on television or in movies. Ignore that image. A mastering studio is something completely different.
Many professional engineers prefer to have their mastering studios away from the recording gear so that they can take a fresh approach to the audio put into their care. This is good for the recording artist, because it allows them to work with more than one person and receive a variety of ideas for the master copy. Another good reason for keeping the mastering gear separate from the recording studio is because many times the devices used in mastering will interfere with the acoustics required for recording.
A quality music mastering studio will have either digital or analog equipment depending on the skills and tastes of the engineer. Some studios will have both. This equipment may include large consoles and monitoring devices. A great studio will be arranged so that the engineer can hear every single detail of a recording.
Each piece of gear has its ups and downs, but both can be used by skilled engineers to create a great master copy. Analog equipment has been around for many years and creates the natural, soft sounds that we remember from the time that records began to be obsolete. In the 90's, though, the digital format began its quick assault of the mastering world due to the ease of adjustment and background noise elimination that this newer technology offers.
No matter what type of technology is available, one truth applies: a great engineer will be able to come up with a great master copy. A nice audio mastering studio is just an additional benefit.